This invention relates to program controlled automatic sewing machines and more particularly to sewing machines for use in sewing closed patterns of different sizes and having spaced apart start and termination points.
Hithertofore, it has been known sewing machines in which a memory medium, such as a magnetic card, magnetic tape or floppy disc stores a sewing pattern and a work holder is moved based on the information of the sewing pattern stored in the memory medium. In such a sewing machine, when a workpiece such as an applique or sticker is sewn onto the workpiece, a so-called work holder with a crank or force transmitting member is employed for moving the workpiece in a manner similar to that disclosed in U.S. Pat. No. 3,104,637.
FIG. 1 shows a sewing machine employing a conventional work holder with a crank or force transmitting member. That is, the work holder 1 is provided on the machine table in a position just below the needle 3 for movement in the directions of both the X and Y axes by pulse motors (not shown). In FIG. 1, reference numeral 5 denotes a turning mechanism. In the normal sewing operation of the sewing machine, as shown in FIG. 2, the turning mechanism 5 moves the work holder 1 which in turn moves the workpiece 6 in the directions of the X and Y axes in conformity with a predetermined sewing pattern. The turning mechanism 5 operates at a predetermined time point after the sewing operation has begun at the sewing start point A to turn a force transmitting or crank member 7 on the work holder 1 from the pattern starting position shown in solid lines in FIG. 2 to the pattern ending position shown in the one-dot and chain line in FIG. 2. When the workpiece 6 has been sewn to the sewing termination point B, the sewing operation on the workpiece completes.
When the crank or force transmitting member 7 is in the pattern starting position shown in solid lines in FIG. 2, the work holder 1 can be moved leftwardly to enable a pattern to be sewn from the start point A through the termination point B to the first inflection point or corner without interference between the crank 7 and needle 3. After the pattern has been sewn past the point B, the crank 7 is rotated from the pattern starting position shown in solid lines in FIG. 2 to the pattern ending position shown in one-dot chain lines in FIG. 2. The work holder 1 can then be moved to sew the pattern through the pattern start point A to the termination point B without interference between the crank 7 and needle 3. This results in the sewing of a closed pattern.
However, in the sewing machine employing the conventional work holder, if the sewing pattern 9 stored in the memory medium is employed in its enlarged scale as shown in FIG. 3, since the sewing pattern is enlarged with the coordinate origin as the center, the sewing start point A and the sewing termination point B on the enlarged sewing pattern 12 are not positioned corresponding to the crank member 7 on the work holder 1 with crank member 7 and thus, the sewing machine having the work holder with crank member has the drawback that the machine can not utilize the sewing pattern enlargement function.
And when the sewing machine having the work holder 1 with crank member 7 is operated employing the sewing pattern 9 stored in the memory medium in a reduced scale as shown in FIG. 4, since the sewing pattern is reduced in scale with the coordinate origin as the center, the sewing start point A and the sewing termination point B on the reduced sewing pattern 13 are not positioned corresponding to the reversion member 7 on work holder with reversion member 1, and thus, the sewing machine also has the drawback that the machine can not employ the reduced sewing pattern function.
And in the conventional sewing machine, in order to return the work holder to the sewing start point when a thread break occurs or abrupt stop in operation occurs due to any cause, the holder is returned along the shortest course between the existing point and return point. Therefore, when using the conventional work holder with crank member, the sewing machine has the drawback that the needle tends to contact the work holder with reversion member to be broken or bent thereby in the course of the returning of the holder to the sewing start point.